The lance tubes of long retracting soot blowers are, in common practice, provided with supporting rollers at a location close to the wall of the boiler or heat exchanger into which the lance tube is projected during cleaning operations. (See, for example, U.S. Pat. No. 3,585,673). When such blowers are so constructed that the lance tube rotates continuously in one direction while advancing, and rotates continuously in the opposite direction while retracting, the helix angle is the same in both directions of movement of the lance tube, and the rollers are typically fixed in such a position that they rotate on the helix line, that is, their axes are fixed in a position perpendicular to the helix line and tangent to a cylinder concentric with the helix. In order to support the lance tube properly, a plurality of rollers are used, including at least two located below and laterally of the axis of the lance tube.
Where the operation of the blower involves changing the helix angle during travel of the lance, as occurs in the operation of blowers having a lance tube which is oscillated about its longitudinal axis during its axial travel, an undesirable degree of sliding friction and resultant wear of the lance tube occur when such rollers are journaled on fixed axes in the manner indicated above. The present invention has as its overall objective the provision of improved roller supporting means which avoids sliding friction between the lance tube and the rollers despite changes of helix angle which occur during operation of the lance tube. A related object of the invention is to provide roller supporting means which is highly sensitive and quickly responsive to changes and reversals of the helix angle, and in which the castering action is virtually unaffected by gravity.
Other objects and advantages of the invention will become apparent to persons skilled in the art upon consideration of the present disclosure in its entirety.